This invention relates to a vehicular ac generator having a bracket having formed in a bracket main body an air intake port rib and an air exhaust port rib for defining a cooling air intake port and exhaust port.
FIG. 9 is a side sectional view of a conventional vehicular ac generator, FIG. 10 is a front view of the front bracket shown in FIG. 9, FIG. 11 is a front view of the rear bracket shown in FIG. 9 and FIG. 12 is a perspective view of a rotor.
This ac generator comprises a case 3 composed of a front bracket 1 and a rear bracket 2 made of aluminum, a shaft 6 disposed within the case 3 and having secured to its one end portion a pulley 4, a rotor 7 of the Rundle type fixed to the shaft 6, a fan 5 secured to the opposite side of the rotor 7, a stator 8 secured to the inner wall surface of the case 3, a slip ring 9 secured to the other end portion of the shaft 6 for supplying an electric current to the rotor 7, a pair of brushes 10 in a sliding-contact relationship with the slip ring 9, a brush holder 11 housing the brushes 10, a commutator 12 electrically connected to the stator 8, a heat sink 16 mounted to the brush holder 11 and a regulator 17 bonded to the heat sink 16 and regulating the magnitude of the ac voltage generated at the stator 8.
The rotor 7 comprises a rotor coil 13 through which an electric current is supplied to generate a magnetic flux and a pole core 14 positioned over the rotor coil 13, where an magnetic poles are formed by the magnetic flux. The pole core 14 is composed of a pair of a first pole core member 18 and a second pole core member 19 meshing with each other. The first pole core member 18 and the second pole core member 19 comprises pawl-shaped magnetic poles made of iron and in the shape of a pawl. The neighboring pawl-shaped magnetic poles 20 and 21 are arranged with a predetermined gap is defined between the magnetic poles so that no flux leakage occurs between the pawl-shaped magnetic poles 20 and 21 and that a cooling air passage for cooling the rotor coil 13 is defined.
The stator 8 comprises a stator core 15 and a stator coil 81 which is an electrical conductor wound on the stator core 15 and in which an ac power is generated due to the change in the magnetic flux in the rotor coil 13 as the rotor 7 rotates.
The rectifier 12 comprises a diode 26 for rectifying the ac current generated in the stator 8 into a dc current and a heat sink 27 for dissipating the heat generated at the diode 26.
As shown in FIG. 10, the front bracket 1 has disposed at an outer circumferential portion of the bracket main body 80 a plurality of exhaust ports 29 formed by a plurality of exhaust port ribs 28. Inside of the exhaust port 29, intake ports 34 are defined by a plurality of intake ribs 35. Also, at the outer circumferential portion of the bracket main body 80, through holes 30 are formed at four positions spaced by 90xc2x0. Bolts 31 are inserted into these through holes 30 and thread-engaged into the rear bracket 2, whereby the rear bracket 2 together with the front bracket 1 holds the stator core 15 therebetween. Also, mounting holes 33 are provided at a pair of mounting leg portions 32 arranged in the V-shape. Bolts (not shown) are passed through the mounting holes 33 and thread-engaged with the engine main body (not shown), whereby the vehicular ac generator is secured to the engine main body.
Also as for the rear bracket 2, as illustrated in FIG. 11, similarly to the front bracket 1, the exhaust ports 29 are defined in the outer circumferential portion of the bracket main body 80 by the plurality of exhaust port ribs 28 and the intake ports 34 are defined in side of the exhaust ports 29 by the intake port ribs 35. Also, mounting leg portions 32 having the mounting holes 33 corresponding to the front bracket 1 are provided.
According to the vehicular ac generator having the above structure, an electric current is supplied form a battery (not shown) to the rotor coil 13 through the brush 10 and the slip ring 9 to generate a magnetic flux, thereby magnetizing the pawl-shaped magnetic pole 20 of the first pawl core member 18 in the N-pole and the pawl-shaped magnetic pole 21 of the second pawl core member 19 into the S-pole. On the other hand, the pulley 4 is driven by the engine and the shaft 6 causes the rotation of the rotator 7 to rotate, so that a rotating field is applied to the stator coil 81 to generate an electromotive force in the stator coil 81. This ac electromotive force is rectified into a dc current through the rectifier 12 and regulated in its magnitude by the regulator 17 to thereby charged in the battery.
The rotor coil 13 and the stator coil 81 always generate heat during the power generation. On the other hand, the fan 5 is rotating for dissipating the heat generated by the power generation.
That is, as shown in FIG. 9, the cooling air sucked in the axial direction through the intake ports 34 on the side of the front bracket 1 flows between the intake port ribs 35 deflected into the centrifugal direction by the fan 5, cools the front side end positron of the stator coil 81 and is exhausted to the outside through the exhaust ports 29 between the exhaust port ribs 28. Also, the cooling air sucked through the intake ports 29 defined between the exhaust port ribs 28 flows between the intake port rib 35, flows through the heat sink 27 of the rectifier 12 and the heat sink 16 of the regulator 17, deflected by the fan 5 in the A centrifugal direction, cools the rear side of the stator coil 81 and is exhausted to the outside through the exhaust ports 29 of the rear bracket 2.
As for the fan 5, the centrifugal fan 5 having a plurality of fan blades 55 is used as illustrated in FIG. 12, so that the air flow is deflected by the fan blades 55 at right angles and exhausted in the axial direction, generating pressure oscillation due to the conflicts between the fan blades 55 and the air at the flow incoming portion, giving an adverse effect in the wind noise. Also, an annular plate 56 fastened to connect the tips of the fan blades together is provided for the purpose of noise reduction.
It is to be noted that the intake ports ribs 29, the exhaust port ribs 35 and the front and rear brackets 1 and 2 not only prevent the ingress of any foreign matter from outside, but also serves and cooling fins for dissipating the heat transmitted from the stator 8 to the front and the rear brackets 1 and 2.
The exhaust port ribs 28 of the front and rear brackets 1 and 2 of this conventional design have not been tilted or inclined in the direction rotation of the rotor by an angle equal to or within 0xc2x0 to 15xc2x0 with respect to the radial line from the rotational axis. Also, the intake port ribs 35 of the front bracket 1 have not had any inclination with respect to the radiation line from the rotational axis. With such the structure, a air flow resistance relative to the direction of the absolute velocity of the cooling air discharged from the fan 5 of the rotor 7 is large and the flow rate has been limited, so that the cooling efficiency has been poor. Therefore, the temperature rise is increased and, as a result, the power output had to be limited. Also, as for the intake ports 34, although the air flows with an inclination due to the whirling component of the incoming air generated by the rotation of the fan 5, the intake port ribs 35 cause the air flow resistance to be large, resulting in the decrease in air flow amount.
Also, since the exhaust port ribs 28 and the intake port ribs 35 have not been in line with the direction of the absolute velocity of the cooling air discharged from the fan 5, the interfering noise was increased.
This invention has been made in order to resolve the above-discussed problems and has as its object the provision of a vehicular ac generator of a low noise and high cooling efficiency and capable of being increased in output power by selecting optimum values of the angles, thickness and the like of the exhaust port ribs and the intake port ribs of the bracket.
In order to achieve the above object, the present invention resides in a vehicular ac generator comprising a case composed of a pair of opposing brackets having exhaust port ribs defining a plurality of exhaust ports and intake port ribs disposed inner side of the exhaust ports and defining a plurality of intake ports; a rotor rotatably disposed within the case; a stator secured within the case and having a stator coil in which an ac current is generated by a rotating magnetic field generated by the rotor; and a pair of fan secured at the axially opposite sides of the rotor for generating a flow of cooling air sucked through the intake ports of the bracket to cool the stator coil and exhausted to outside from the exhaust ports; characterized in that the exhaust port ribs of at least one of the brackets are tilted from 20xc2x0 to 50xc2x0 in the direction of rotation of the rotor with respect to the radial direction of the generator.
The rib thickness of the exhaust port ribs in the normal plane of the tilt direction of the exhaust port ribs may be equal to or less than 50% of the exhaust port width.
When the rotor rotates the fan rotates to suck air from the intake ports of the bracket which cools the rear side end portions and the front side end portions of the stator coil and which exhausts from the exhaust ports. The air exhausted from the exhaust ports is exhausted at a predetermined angle with respect to the radial line from the rotary axis due to the whirling component due to the rotation of the fan.
According to experiments, as the tilt angle of the exhaust port ribs is increased, the power output increases up to about 50xc2x0 which is believed to be the most preferable angle and, the further increase of the tilt angle causes the output to sharply decrease. On the other hand, the wind noise sound pressure sharply is decreased up until about 20xc2x0, kept about constant from 20xc2x0 to 60xc2x0 and has a transition point at about 60xc2x0 from where it is decreased again.
Therefore, when the tilt angle of the exhaust port ribs is set at from 20xc2x0 to 50xc2x0 in the direction of rotation of the rotor, both the power output and the wind noise can be made satisfactory.
Also, the rib thickness of the exhaust port ribs in the normal plane of the tilt direction of the exhaust port ribs may preferably be equal to or less than 50% of the exhaust port width.
According to the experiments, as the rib thickness relative to the exhaust port width is increased, the power output is gradually increased and, with a transition point at about 0.5, it is sharply decrease. Contrary to this, the wind noise does not change much because the angle is set at from 20xc2x0 to 50xc2x0 which is close to the velocity vector of the exhausted cooling air.
The intake port ribs of at least one of the brackets may be tilted from 25xc2x0 to 35xc2x0 in the direction opposite to the direction of rotation of the rotor with respect to the radial line from a rotational axis.
As for the intake ports, the air flow is also sucked at a predetermined tilt angle with respect to the radial line from the rotary axis due to the whirling component due to the rotation of the fan, so that there is an optimum angle as in the exhaust port ribs. According to the experiments, when the tilt angle of the intake port ribs is set at from 20xc2x0 to 50xc2x0, both the power output and the wind noise can be made satisfactory.
Also, the side surfaces of the intake port ribs on side of the rotational direction of the fan may preferably be tilted from 10xc2x0 to 20xc2x0 with respect to the axis in a plane perpendicular to the intake port ribs.
With such arrangement, the incoming air flow is smoothly introduced.
The ratio of the width in the circumferential direction of the intake port may be made equal to the ratio between the diameter of the innermost edge of the ports and the diameter of the outermost edge of the ports.
Also, a taper of from 40xc2x0 to 50xc2x0 may be provided in the inner circumferential surface on the outermost diameter side of the intake port so that the diameter gradually decreases from the outer air side toward the case inner portion.
Further, the fan may be provided with an annular plate connecting the tip of each fan blade and wherein the taper in the inner circumferential surface on the outermost diameter side of the intake port is formed with the inner diameter of said annular plate used as the base point.